The studies supported by this grant are designed to increase the sophistication of our understanding of the mechanisms of cellular movements by analyzing the molecules involved. In 1980-81 we will characterize proteins from Acanthamoeba which promote and inhibit actin filament cross-linking. By direct electron microscopic observation we will study the mechanism of actin filament assembly by measuring rate constants for the steps in polymerization. Using electron microscopic crystallography we will determine the structure of the actin molecules to a resolution of about 1 nm.